The invention relates to a communication system having of at least two private branch exchanges, each having a switching control unit and at least one switching node, which is connected, via a network terminal means, to at least one higher-level communication network. It is connected, via at least one subscriber terminal means, to terminal. A team function control unit is provided in one of the private branch exchanges, which control unit controls, according to a team function, particular terminal apparatuses as team terminal apparatuses of a team. These apparatuses can be called via the switching node of this private branch exchange. The team function control unit occasions a signaling to other team terminal apparatuses dependent on the switching-oriented state of individual team apparatuses, and influences the switching-oriented state thereof.
One embodiment of private branch exchanges connected with one another, in at least one of which a team function is realized, is the private branch exchange HICOM 300, marketed commercially by Siemens AG. A known team function is for example the function `call pickup,` in which incoming calls are displayed within a call pickup group of several terminal apparatuses and can be received at each terminal apparatus belonging to the call pickup group. Another known team function is the function `PBX line group,` which can be reached at a special line group number. Each subscriber of a line group can also be called immediately via an individual call number. However, all subscribers are reached via the special line group number. The line group number is for example allocated to a master terminal apparatus.
A further known team function is the integrated secretarial unit, also called the executive secretary unit.
In known communication systems, all subscribers of a team are connected to a single private branch exchange, and are switched to a higher-level communication network via the same network terminal means.